You intuitively know that all of those applications running in the background on your phone are latently eating away at your battery's charge, but a new study reveals that the main culprit isn't any useful function. It's location-pinging ads.

The study, conducted by a team lead by Abhinav Pathak from Purdue University, analyzed the energy used by several popular free Android apps (PDF) like Angry Birds, Facebook, the New York Times, and Chess. The team developed an "energy profiler" they call "Eprof" that determines what processes within an app are using energy. The results are shocking: 65 to 75 percent of energy consumed by the free apps studied are used by third-party advertising modules within the programs. These apps continue to run in the background even when you're not actually using the app. Only 10 to 30 percent of that energy is used to power the applications' "core functions."

Apps shouldn't continue to serve you ads when you're not locking at the apps. It's a bug, or something more nefarious. According to the researchers, developers don't notice energy consumption problems—bugs or otherwise—because most apps are "energy oblivious," meaning that the developers don't pay attention to how much energy apps use. [Eurosys 2012 via New Scientist]